The present invention relates generally to an alarm device incorporating a code verification system and, more particularly, includes a code verification system which is adapted to verify a code at the point of entry of the code and to transmit an alarm signal to a receiving station if an incorrect code is entered into the system.
At present, many burglar alarm systems include a central office that is connected to remote subscribers by telephone lines and the like. In operation, when a subscriber enters a protected premises, the subscribers must transmit a preselected code to the central office to prevent an alarm condition. That is, if the preselected code is not received within a predetermined time interval after entry onto the protected premises, an alarm will be produced at the receiving station.
The code usually comprises a plurality of decimal digits which are transmitted in the form of pulses equal in number to the particular code. That is, if the code to be transmitted is, for example, "32", three pulses will be transmitted followed by a transmission of two pulses. The subscriber produces the pulse code by depressing a button first three times and then two times.
The code may be detected at the receiving station either manually or automatically by use of a computer and the like. However, both of these methods have serious disadvantages associated with their use. To be more specific, in manually or non-computer operated central offices or receiving stations, code verification in usually made by a person who counts the number of times a meter needle moves between two levels. Depending upon the length of the identification code and the speed with which it is produced, a large amount of human error is possible. Accordingly, if the code "seems correct" the observer at the receiving station may very well accept the code as a correct code although the code may, in fact, be incorrect and may have been transmitted by unauthorized personnel. Similarly, the observer may produce an alarm signal even though a correct code has been transmitted.
In a computer-operated central office, the entire code is usually received before the data is processed. Accordingly, a finite delay will be encountered before a particular code can be verified and an incorrect code called to the attention of an observer to signal an alarm condition. In many cases, such delay may permit unauthorized personnel to evacuate the premises before any action can be taken. Accordingly, an object of the present invention is to provide an improved alarm device or system having an entered code verification system.
A more specific object of this aspect of the invention is to provide a code verification system at the point of entry of the code, thereby eliminating the time consuming need to search a memory bank to verify the correctness of the code.
Another object of this invention is to provide an alarm device having a code verification system that acts immediately to transmit an alarm condition to the central office or receiver upon entry of an incorrect code.
A further object of the invention resides in the novel details of circuitry that provides an alarm device having a code verification system of the type described that may be utilized in conjunction with existing code generating systems.
A further object of the invention is the provision of a code verification system in an alarm device that is adapted to transmit a signal to the central office upon entry of an incorrect code which signifies that a hold-up is in progress.